Backpack



FIG. 1 is a front view of a backpack showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a perspective view thereof.

The broken lines in the figures are for the purpose of illustrating environment and form no part of the claim. 

CLAIM The ornamental design for a backpack, as shown and described. 